Electric discharge device



March 1960 E. H. ULLRICH ET AL 2,928,976

ELECTRIC DISCHARGE DEVICE 2 Sheets-Sheet 1 Filed Feb. 2, 1955 F/Gl.

Inventor: E. H. ULLRICH G. F. KLEPP By Attorney March 15, 1960 E. H. ULLRICH ETAL 2,928,976

ELECTRIC DISCHARGE DEVICE Filed Feb. 2, 1955 M n/ n n r I8 20 3 v 9 l9 2 2 lnventon E. H. ULLRICH' G F, KLEPP wiiflm Atlomey 2 Sheets-Sheet 2 ELECTRIC DISCHARGE DEVICE Edward Hill Ullrich and George Francis Klepp, London, England, assignors to International Standard Electric Corporation, New York, N.Y.

Application February 2, 1955, Serial No. 485,737

Claims priority, application Great Britain February 18, 1954 1 Claim. (Cl. 313-188) The present invention relates to gas-filled electric discharge tubes containing, within the same envelope, electrodes defining two or more discharge gaps. In the construction of multi-electrode tubes, of whatever type, special attention must be paid to the mounting of the various electrodes in correct positions relative to one another and to the external envelope of the tube, and to maintaining correct positioning of the various members during the life of the tube. The supporting members must provide insulation between the various electrodes and normally the supportingmembers will be made largely of insulating material. In gas-filled glow discharge tubes it is frequently necessary, in addition to supporting the electrodes in their correct relative positions insulated from one another, also to ensure that glow discharge does not spread beyond certain prescribed areas. This is particularly the case with respect to cathode electrodes; thus a cathode in a glow discharge tube may be constructed from a stamped-out piece of metal sheet of which, however, only a small area is to be subject to the glow discharge. Among other means which may be adopted, a simple and often practical way of restricting spread of glow discharge to a specified surface area is to sandwich the electrode between sheets of insulating material. with the portion to which glow discharge is desired projecting beyond the edges of the insulating sheets. It is particularly convenient, if possible, to use sheets of mica on which to mount electrodes, as then the construction may follow, very largely, conventional radio receiving tube practice.

In certain types of glow discharge tube the use of sheets of insulating material, particularly mica, to which to secure electrodes of different discharge gaps, though mechanically convenient, is open to great objection in that charges are liable to collect on the surfaces or edges of the insulated sheets and thereby to upset the normal performance of the tube. In addition, particularly where mica is concerned, there is the danger that undesired contamination of electrode surfaces may arise, due to liberation of gas from the insulating surfaces or edges. In a glow discharge, insulating material within the field of the discharge may be subject to quite severe ionic bombardment and however carefully de-gasing processes may have been applied during manufacture of the tube, under conditions of bombardment mica is very liable to some surface disintegration and gasification, while, at the same time, absorption of some of the gas filling or of materials sputtered from the cathode may easily arise; also the insulation resistance of the material separating adjacent electrodes may become impaired and the liabi ity to acquire spurious charges may be increased. Thus, in one type of multi-cathode tube in which it is arranged that discharge occurs from one cathode at a time to a common anode and, by means of pulses applied to certain of the electrodes in common, the discharge is stepped from cathode to cathode along an array of discharge gaps, it was found that, occasionally, on application of a transfer pulse, the glow discharge, instead of stepping on to the next cathode, would either overstep, so that it finally came to rest on the cathode beyond that on which it should have stayed, or would understep, in which case a discharge was transferred back along the array to a previous cathode.

For a long time this defect defied any'explana'tion or remedy, until it was observed that it was subject to a time delay after the application ofthe transfer pulse, the delay being comparable with that obtained with a simple. R.C. circuit having a shunt resistance path of several megohms. Attention was thus directed to the surfaces and edges of the mica insulating sheets between which the cathodes were sandwiched. We found that spurious effects could be completely eliminated by inter-posing some discontinuity in the micas between adjacent gaps, either by coating a narrow segment with conducting material and earthing this coating, or by providing slots in the micas between the adjacent gaps.

In accordance with the present invention there is provided a gas filled electric discharge tube having electrodes defining two or more dischargev gaps, the said electrodes being mounted on a sheet of insulating material in'such manner that a region of the surface or edge of the said sheetunder at least some conditions of operation of the said tube lies in the field of the discharge at a said gap, characterised in this that means are provided for preventing electric discharges being retained on thesaidsurlar array of cathodes for a multi-cathode glow discharge face or edge between the adjacent gaps.

An embodiment of the invention will be described with reference to the accompanying drawings in which:

Fig. 1 is an exploded view of the assembly of a circutube; Fig. 2 shows part of the completed discharge tube with certain members sectionaii'zed to show the cathode assembly in relation to the anode and envelope of the tube; and Fig. 3 is an enlarged view of part of Fig. 2 showing the application of the present invention.

In Fig. lthe members 1 are approximately sectorshaped parts of sheet metal "which we shall refer to as storage cathodes. carry rectangular, extensions 2 which are bent over at right angles to the plane of the sectors. These projections 2, together with the adjacent peripheral edges 3 of the sectors, provide the desired discharge surfaces for the respective storage cathodes. The bent over portions 2 are referred to as cathode plates and the edge portions 3 as cathode tails. A further set of electrodes, known as transfer cathodes, are provided by a sheet metal spider 4, arranged to lie in the same plane as the cathodes 1, with a leg of the spider between each pair of adjacent storage cathodes. Each leg of the spider carries a bent over trapezoidal projection 5 which, in the assembled tube, lies on the same cylindrical surface as the cathode plates 2 and it is desired that the effective discharge surface of the transfer cathodes be restricted to the outer surfaces of the bent-over portions 5. Both storage and transfer cathodes are provided with small projecting dimples such as indicated at 6, which engage in corresponding holes 7 in a mica washer 8. The cathodes are retained in position by means of an upper mica disc 9, the assembly being clamped between lower and upper shields 10 and '11, respectively, by means of tie rods (not shown) which pass through respective sets of aligned holes in the various members, in holes such as 12, 13, 14, i5 and 16 in the respective members 10, 8, 1, 9 and 11. Both upper and lower shields are cup-shaped, the wall 17 of the lower shield 10 being arranged. to lie just underneath the bentover portions 2 and 5 of the storage and transfer cathodes respectively, while the wall 18 of shield 11 lies on the surface of an imaginary cylinder containing the outer surfaces of the bent-over cathode portions 2 and 5. The

'On; their outer periphery the members shields 1G and 11 are designed,- by their" proximity to the cathode discharge surfaces, to confine glow discharge to the front surfaces of the respective portions 2 and 5. In this function they are assisted by the outer edges of the washer? and 'disc 9. The arrangement of the cathode with respect to the anode will be seen from Fig. 2, in which a cylindrical anode 19 is shown surrounding the cathodes and supported from the cathode assembly by means of a mica disc 26, secured above the shield 11. The tierods referred to above as securing the cathode assembly also secure theanodew and are indicated at 21 in Fig. 2, the complete electrode assembly being mounted upon a further mica Washer, not shown, which positions the assembly with respect to a surrounding glass envelope 22.

During operation it is arranged that glow discharge may be maintained between the anode and any one storage cathode. Due to difference in shaping of the cathode-tail and plate portions the glow discharge is maintained only over the plate portions 2, the gap anode cathode tail 3 having a higher maintaining potential than the gap anodeplate 2. The transfer cathodes are normally biased .to a potential more positive than that of the storagev cathodes to prevent them from sharing in the discharge to the stor-j age cathodes. On receipt of a transfer pulse, the transfer cathodes are driven more negative than the storage cath odes and discharge occurs from that transfer cathode immediately adjacent the glow which has been maintained at one of the cathode plates. It is arranged'that the dis charge at a transfer cathode extinguishes the previously existing discharge of the adjacent cathode plate while, at the end of the transfer pulse, the glow is transferred to the adjacent cathode tail, along which it spreads onto the adjoining cathode plate portion and is there main-' tained until the arrival of a next transfer pulse. The discharge is thus stepped by the transfer pulses from storage cathode to storage cathode along the array and in the direction from cathode tail to. cathode plate of the same cathode. i i

In tubes prior to the present invention, the edges of the mica insulators 8 and disc 9 between adjacent cathodes were continuous. Both edges adjacent the cathode plate from which the glow discharge'was being maintained were immediately adjacent the cathode glow and hence became subject to the ionic bombardment and sputtered deposits mentioned earlier herein; 7

In accordance with the present invention, however, the effect of this is overcome by" providing slots 23 and 24 in the respective mica insulators between each pair of adjacent cathodes, the position of the slots being clear- 1y visible in Fig. 3, which shows the geometrical arrangement of the cathode assembly.

Although the invention has been described above with specific reference to a particular type of rnulti-cathode tube, using mica insulators, it is evident that the invention can also usefully be applied to other types of tubes, such for exampleas a double-trigger tube, in which subsidiary electrodes are provided to form with either cathode or anode a pair of auxiliary discharge gaps of lower striking potential than the main cathode-anode gap of the tube. Furthermore, use of the invention is not restricted to cases where mica is involved, but may also be applied where ceramic or even glass insulation is used. Particularly in the latter case it may be more convenient to provide, instead of the'slots illustrated in the embodi ment described above, small areas between adjacent gaps of conductive material coated upon the insulators bridging the gaps.

- While the'principles of the invention have been described above in connection with specific embodiments, and particular modifications thereof, it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope'of the invention.

.What we claim is:

An electric discharge tube comprising an envelope con taining therein an ionizable gas, a sheet of insulating material,-a plurality of electrodes mounted on said sheet in spaced relation with each other and defining a plurality of glow-discharge gaps thereamong, the areas of said sheet between adjacent electrodes defining regions which lie in the field of their adjacent discharge gaps, said sheet comprising means for inhibiting ionic bombardment and sputtering of said regions, thereby preventing the reten: tion of electric charges in said sheet, said inhibiting means comprising a plurality of slots in said sheet of insulating material located respectively between adjacent discharge gaps.

References Cited in the file of this patent UNITED STATES PATENTS 7 1,763,108 Spencer June 10, 1930 2,142,106 Boswau Jan. 3, 1939 2,160,044 Warren -Q Ma'y'30, 1939 2,171,230 Wamsley Aug. 29, 1939 2,213,558 Veeneman Sept. 3,1940 2,512,858 Hegbar June 27, 1950 2,524,213 Wales Oct. 3, 1950 2,553,585 Hough May 22,1951 2,559,426 Hasselhorn July 3, 1951 

